Golf balls generally include a spherical outer surface with a plurality of dimples formed thereon. Conventional dimples are circular depressions that reduce drag and increase lift. These dimples are formed where a dimple wall slopes away from the outer surface of the ball forming the depression.
Drag is the air resistance that opposes the golf ball's flight direction. As the ball travels through the air, the air that surrounds the ball has different velocities thus, different pressures. The air exerts maximum pressure at a stagnation point on the front of the ball. The air then flows around the surface of the ball with an increased velocity and reduced pressure. At some separation point, the air separates from the surface of the ball and generates a large turbulent flow area behind the ball. This flow area, which is called the wake, has low pressure. The difference between the high pressure in front of the ball and the low pressure behind the ball slows the ball down. This is the primary source of drag for golf balls.
The dimples on the golf ball cause a thin boundary layer of air adjacent to the ball's outer surface to flow in a turbulent manner. Thus, the thin boundary layer is called a turbulent boundary layer. The turbulence energizes the boundary layer and helps move the separation point further backward, so that the layer stays attached further along the ball's outer surface. As a result, a reduction in the area of the wake, an increase in the pressure behind the ball, and a substantial reduction in drag are realized. It is the circumference of each dimple, where the dimple wall drops away from the outer surface of the ball, which actually creates the turbulence in the boundary layer.
Lift is an upward force on the ball that is created by a difference in pressure between the top of the ball and the bottom of the ball. This difference in pressure is created by a warp in the airflow that results from the ball's backspin. Due to the backspin, the top of the ball moves with the airflow, which delays the air separation point to a location further backward. Conversely, the bottom of the ball moves against the airflow, which moves the separation point forward. This asymmetrical separation creates an arch in the flow pattern that requires the air that flows over the top of the ball to move faster than the air that flows along the bottom of the ball. As a result, the air above the ball is at a lower pressure than the air underneath the ball. This pressure difference results in the overall force, called lift, which is exerted upwardly on the ball. The circumference of each dimple is important in optimizing this flow phenomenon, as well.
By using dimples to decrease drag and increase lift, almost every golf ball manufacturer has increased their golf ball flight distances. In order to optimize ball performance, it is desirable to have a large number of dimples, hence a large amount of dimple circumference, which is evenly distributed around the ball. In arranging the dimples, an attempt is made to minimize the space between dimples, referred to herein as “land area”, because the land area does not improve aerodynamic performance of the ball. In practical terms, this usually translates into 300 to 500 circular dimples with a conventional sized dimple having a diameter that typically ranges from about 0.100 inches to about 0.180 inches.
One attempt to improve the aerodynamics of a golf ball is suggested in U.S. Pat. No. 6,162,136, wherein a preferred solution is to minimize the land surface or undimpled surface of the ball to maximize dimple coverage. One way of maximizing the dimple coverage of the ball is to pack closely together circular dimples having various sizes, as disclosed in U.S. Pat. Nos. 5,957,786 and 6,358,161. In practice, the circular dimple coverage is limited to about 85% or less when non-overlapping dimples are used.
Another attempt to maximize dimple coverage is to use polygonal dimples with polyhedron dimple surfaces, i.e., dimple surfaces constructed from planar surfaces, as suggested in a number of patent references including U.S. Pat. Nos. 6,290,615, 5,338,039, 5,174,578, 4,830,378, and 4,090,716, among others. Theoretically, higher dimple coverage is attainable with these polygonal dimples, as the dimples may be tessellated, i.e., the dimples are arranged in a tiled pattern with generally uniform land widths between the dimples.
In non-tessellated dimple configurations, the land areas have cross-sectional shapes that vary with position in an uncontrolled manner. The width and edge angle associated with a given location of land area is simply an unintended consequence of the dimples that surround it.
Hence, there remains a need in the art for a golf ball that has a high dimple coverage and superior aerodynamic performance.